I did Judo for a while as a teenager; when I started AJJ I thought it would help alot but actually the cross-over in terms of techniques was fairly minimal. There is much less emphasis on throws in AJJ and because there is no competition the training sessions tend to be less physically taxing. However, I prefer AJJ because it is budo rather than sport and Judo will teach you things that are only really practical for Judo. For example you don't want to be grappling with someone in the street newaza style if you can help it, also it someone has a weapon your judgement of distance and safety will have to change. You need to be in close for Judo to work effectively; the 'grip' is very important in Judo to gain the upperhand over your opponent. Sometimes that is disadvantageous in a self-defence situation. I remember when I did Judo as a teenager I asked my sensei once how to use Judo in self-defence and he said he wouldn't use it for self-defence. I think AJJ is more well-rounded as a martial art. If you want to cross-train in Judo and Aikido do it, but they are very different.